A printing machine is equipped with a sheet feeder, a printing unit, a paper discharge device, and an ink unit, and this printing unit is in contact with a blanket cylinder, an impression cylinder, a transfer cylinder, a plate cylinder and the like, and supported on a shaft. The inking unit is provided with a group of rollers including ink forming rollers corresponding to the plate cylinder, and ink fountains.
A plurality of the ink forming rollers contact a single plate cylinder, individually applying ink of different colors to the plate cylinder. The ink forming rollers are provided with patterns according to the printed matter, and, therefore must be replaced when the printed matter is changed or the roller surface is worn out.
Prior art ink forming rollers are rotatably supported on the frames, and one end of each cylinder is supported by a moving shaft which is supported on the frames and movable in the axial direction. The moving shaft is mounted with a hydraulic cylinder to which a hydraulic pump is connected. The ink forming rollers are replaced by operating the hydraulic cylinder to move the moving shaft, allowing removal of the ink forming rollers from the frames.
Such ink forming rollers are removed by moving the moving shaft in the axial direction by means of the hydraulic cylinder. Therefore the positional holding of the ink forming rollers depends on the hydraulic cylinder. If the hydraulic pump stops due to a power failure or the like, the pressure of the hydraulic cylinder decreases. As a result, the retaining force on the moving shaft, and, in turn, on the ink forming rollers is decreased, and the ink forming rollers can fall down from the frames due to their weight.
Furthermore, since the operation of the hydraulic cylinder is controlled by the pressing of a button by an operator, if the operator presses the button by mistake during operation of the printing machine, there may occur defective printing or damage to the ink forming rollers or even damage to the printing machine.
To prevent this, a safety pin has been provided in order to prevent the ink forming rollers from falling down even when the hydraulic pump stops or due to the operator's misoperation. Therefore, when the ink forming rollers are mounted, this safety pin is moved by the operator to lock the ink forming rollers, thereby retaining the ink forming rollers in position. When the safety pin is moved to an unlock position to unlock the ink forming rollers, the rollers can then be replaced.
Such a safety pin is provided to prevent the ink forming rollers from falling down due to a stoppage of the hydraulic pump or the operator's misoperation. However, since the safety pin is operated manually by the operator, the operator may fail to move the pin to the lock position when the ink forming rollers are mounted. In such a case, the ink forming rollers cannot be prevented from falling down due to a stoppage of the hydraulic pump or the operator's misoperation, and the ink forming rollers or even the printing machine may be damaged.